Device for finding centroid coordinates of figures

Abstract: A device for finding the centroid coordinates of a figure that can calculate the centroid from a single time measurement of the figure and display the calculated centroid of the figure. The measuring device comprises a main body having a roller capable of running in a single direction and a measuring lever pivotably supported by the main body so as to be rotatable right or left from the running direction of main body on a horizontal plane. In the measuring device, the main body has a display and a calculating circuit. The tracer of the measuring lever traces the contour of the figure to measure the coordinates, areas, and lengths of the figure. At the same time, the calculating circuit computes the geometrical moments of areas successively and sums the geometrical moments of the areas. Finally, the calculating circuit divides the summed geometrical moment of the areas by an area of the figure to obtain the coordinates of the centroid of the figure. The display is showing the differences of the current coordinates of the measuring lever from the coordinates of the centroid of the figure.

Description: FIELD OF THE INVENTION This invention relates under a more general aspect to a measuring device for a figure. Under a more special aspect this invention relates to a device for finding the centroid coordinates of a two dimensioned figure according to the precharacterizing part of claim 1. BACKGROUND OF THE INVENTION A device for measuring a figure such as a linear planimeter etc. for measuring the area of a figure, coordinates of a figure or length of a curve on a figure comprising the features of the precharacterizing part of claim 1 is known from EP 0 197 173 of same applicant. In the prior art, when finding a centroid of a linear figure a-g-f-e-d-c-b-a as shown in Fig. 3, for example, the figure is divided into sub-figures having known figure centroids, such as triangles a-b-g, b-g-f, and b-f-h and rectangle c-d-e-h, or a square, geometrical moments of their areas are individually calculated and summed up, and the summed moment is divided by the total area of the linear figure. When finding the centroid of a curved figure as shown in Fig. 4, for example, the only way to obtain its centroid is by dividing the figure into a multiple of approximate triangles and applying the same method as above. However, when finding linear figures such as those of Fig. 3, the prior method takes a long time because the amount of calculations increase with the number of sides, although it can obtain an accurate centroid. Further the prior method can hardly obtain an accurate centroid for a curved figure as shown in Fig. 4 because it uses the approximation method. To obtain an accurate centroid, the figure has to be divided more finely. This is practically impossible to do manually. In view of solving the foregoing problems of the prior art, it is an object of the present invention to provide a device for finding the centroid coordinates of figures that can calculate the centroids at a single time of measurement of the figure and can display the calculated centroid on the figure. SUMMARY OF THE INVENTION Briefly, the foregoing object is accomplished by a device for finding the centroid coordinates of a figure according to the present invention. The device comprises a main body having a roller capable of running in a single direction and a measuring lever pivotably supported by the main body so as to be rotatable right or left from the running direction at the main body in a horizontal plane. In the device, the main body has a display, and a calculating circuit. A tracer of the measuring lever traces the contour of the figure to measure the coordinates, areas and lengths of the figure to be measured. At the same time, the calculating circuit computes the geometrical moments of an area successively and sums the geometrical moments of the area, and finally, the calculating circuit divides the summed geometrical moment of the area by an area of the figure to obtain the coordinates of the centroid of the figure. The display shows the differences of the current coordinates of the measuring lever from the coordinates of the centroid of the figure and the measuring lever is moved until the display indicates zero differences, thereby showing coordinates of the centroid of the figure. Also, in the device of the present invention, the measuring lever includes a marking needle near the trace. The display shows the differences of the coordinates of the position of the marking needle from those of the figure centroid and the marking needle is moved until the display indicates zero, thereby showing the coordinates of the centroid of the figure. As described above, the device for finding the coordinates of the centroid of a figure according to the present invention can determine the centroid as follows. As the tracer is moved along the contour of the figure, the device measures the areas of the figure. At the same time, the device successively calculates the geometrical moments of the areas. At the end of the figure measurements, the device divides the sum of the geometrical moments by the area of the figure, thereby obtaining the centroid. The operation of the device is based on the theory described below. In Figs. 5 and 6, for example, the geometrical moment Mx of the area for the x-axis can be given by where D is the domain of y = f(x). The y-coordinate of the figure centroid can be obtained by dividing the geometrical moment Mx by the area A of domain D. Similarly, the x-coordinate of the figure centroid can be obtained by dividing the geometrical moment My by the area A of domain D. where the geometrical moment Mx of the area is A union of domains D and E is zero. This means that even if no geometrical moment of domain D is obtained directly, the geometrical moment of smaller domain E is subtracted from that of larger domain (D + E), leaving the geometrical moment of domain D. Actual figures are hardly given in terms of functions like y = f(x) . For the reason, while tracing the figure contour, the contour is divided into minute sections and the geometrical moments of the minute areas are calculated successively and the whole geometrical moment of the area is obtained. The foregoing and other objects, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a plan view of an embodiment of a device for finding the centroid coordinates of figures according to the present invention; Fig. 2 is a pattern having a linear contour to explain the measurement of the figure centroid according to the present invention; Fig. 3 is a pattern having a linear contour to explain the measurement of a figure controid by prior art methods; Fig. 4 is a curved contour pattern to explain the measurement of a figure centroid by prior art methods; Fig. 5 is a pattern to explain the theory of measurement of the figure centroid according to the method of the present invention; Fig. 6 is another pattern to explain the theory of measurement of the figure centroid according to the method of the present invention; and Fig. 7 is a flow chart showing the operation of the device for finding the centroid coordinates of a figure according to the present invention. Reference Numerals in Drawings refer to: 1 = main body 2 = measuring lever 3 = display 4 = input unit 5 = roller 6 = tracer 7 = marking needle DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The following describes in detail an embodiment according to the present invention with reference to the accompanying drawings. Fig. 1 is a plan view of an embodiment of a device for finding the centroid coordinates of a figure. The device is comprised of main body 1 having roller 5 capable of running in a single direction and measuring lever 2 pivotably supported by main body 1 so as to be rotatable right or left from the running direction of main body 1 on a horizontal plane. Main body 1 has display 3, input unit 4, and calculating circuit thereinside. Measuring lever 2 has tracer 6. Tracer 6 traces the contour of a figure to measure the coordinates, areas, and lengths of the figure. At the same time, the calculating circuit computes the geometrical moments of areas successively and sums the geometrical moments of the areas. Finally, the calculating circuit divides the first moment of the areas summed by the area of the figure to be measured to obtain the coordinates of the centroid of the figure. Display 3 shows the differences of the current coordinates of measuring lever 2 from the coordinates of the centroid of the figure. Measuring lever 2 is moved until display 3 indicates zero differences, thereby showing the coordinates of the centroid of the figure. Measuring lever 2 has marking needle 7. Display 3 shows the differences of the coordinates of the position of marking needle 7 from those of the centroid of the figure. Marking needle 7 is moved until display 3 indicates zeros, therefore marking needle 7 indicates the coordinates of the centroid of the figure. Measuring lever 2 also includes push button switches 8 and 9. For measuring a linear figure, as described hereinafter, activating push button 8 makes tracer 6 read the coordinates where tracer 6 is positioned. For measuring a curved figure, activating push button 9 makes tracer 6 continuously read the coordinates of tracer 6 as tracer 6 traces the contour of the curved figure. In turn, the following describes the operation of successive calculations of the geometrical moment of the area for the x-axis of an n-polygon shown in Fig. 2, To obtain the geometrical moment of area My 1 of a trapezium P 1 P 2 x 2 x 1 , the trapezium is divided into two triangles P 1 P 2 x 1 and P 2 x 2 x 1 , and the following equation is used. My 1 = (x 2 - x 1 )(y 2 2 + y 2 y 1 + y 1 2 )/6 A geometrical moment My n of the area of a trapezium formed of a n-th sides can be given by My n = (x n+1 - x n )(y n+1 2 + y n+1 y n + y n 2 )/6 Note that Eq. 1 above is applicable to a clockwise trace. For a counterclockwise trace, the sign should be inverted. Similarly, the geometrical moment Mx n of the area for the y-axis of a trapezium formed of a n-th sides can be given by Mx n = (y n - y n+1 )(x n+1 2 + x n+1 x n + x n 2 )/6 Note that Eq. 2 above is applicable to a clockwise trace. For a counterclockwise trace, the sign should be inverted. Also, note that point P n+1 (x n+1 , y n+1 ) coincides with point P 1 (x 1 , y 1 ) to close the figure. If the device successively traces all the coordinates of vertexes P 1 , P 2 , ..., P n , and P n+1 , geometrical moments of area My and Mx for the x-axis and y-axis can be respectively obtained by These equations mean to subtract the geometrical moments of smaller area E from the respective moments of larger area (D + E), leaving the geometrical moments Mx and My of area D to be measured. In general, area S of the figure can be obtained by where F > 0 for a counterclockwise trace or F < 0 for a clockwise trace. S = |F|/2 where |F| is an absolute value of F. Coordinates G(x, y) of the centroid of the figure shown in Fig. 5 can be obtained by dividing geometrical moments Mx and My of area by area S of the figure. Note that the trace turning direction can be seen by checking the sign of F. It is not needed to limit the turning direction the tracing should take. Fig. 7 is a flow chart showing the operation described above. When tracer 6 reaches each vertex of the linear figure, push button switch 8 is pushed and the coordinate of each vertex is measured and at the same time the calculating circuit computes geometrical moments My n and Mx n and F n . Finally the calculating circuit divides the summed geometrical moments of the areas by the total area of the figure to obtain coordinates of the figure centroid. When measuring the centroid of a curved figure, push button switch 9 is pushed and tracer 6 continuously reads the coordinates of the contour of the figure as it traces the figure contour. A number of the coordinates are used to calculate Eq.3, 4 and 5 and obtain the centroid of the figure. A large number of coordinates means that n in the equations becomes large enough (nearly infinite) that coordinates of centroid obtained approach real values. As described so far, the present invention provides the feature that allows the device according to the present invention to obtain the centroid of both linear figures and curved figures and can automatically display the centroid of the figure by tracing only the contour of a curved figure or reading the vertexes of a linear figure. While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of invention.

Claims: A device for finding the centroid coordinates of a two dimensional figure comprising a main body (1) having roller means (5) capable of running in a single direction; a measuring lever (2) pivotably supported by the main body (1) so as to be rotatable right or left from the running direction of the main body (1) in a horizontal plane, the measuring lever (2) having a tracer (6) to trace a contour of the figure to measure the coordinates, areas, and lengths of the figure to be measured; the main body (1) including a display (3) and a data processing means, characterized in that the data processing means is a calculating circuit which is adapted to compute the geometrical moments of geographical areas successively at the same time the measuring lever (2) is tracing, to sum the geometrical moments of the geographical areas, and to divide the summed geometrical moments of the geographical areas by the area of the figure to obtain the coordinates of the centroid of the figure; the display (3) is adapted to show the differences of the current coordinates of the measuring lever (2) from the coordinates of the centroid of the figure, and the measuring lever (2) is adapted to be moved to the centroid of the figure so that the display (3) indicates a zero difference. The device for finding the centroid coordinates of a figure according to claim 1 wherein: the measuring lever (2) includes a marking needle (7) near the tracer (6), the display (3) is adapted to show the differences of the coordinates of the position of the marking needle (7) from those of the centroid of the figure, and the marking needle (7) is adapted to be moved to the centroid of the figure so that the display (3) indicates zero, thereby showing the coordinates of the centroid of the figure. Apparatus for measuring the coordinates of the centroid of a two dimensional figure comprising a main body (1) roller means (5) on said main body (1) adapted to roll said main body (1) in a single direction, a measuring lever (2) pivotably supported on said main body (1), said measuring lever (2) being rotatable in a horizontal plane to the right and left of the rolling direction of said main body (1), tracer means (6) on said pivotably supported measuring lever (2), adapted to trace the contour of a figure to measure the coordinates, areas and length of said figure; data processing means, characterized in that the data processing means is a calculating means in said main body (1) adapted to calculate the coordinates from predetermined equations, said calculating means being adapted to successively calculate and sum the geometrical moments of areas as they are being traced by said tracing means on said measuring lever (2) and to divide the sum of the moments of the geographical areas by the area of said figure to obtain the coordinates of the centroid of said figure; display means (3) adapted to display inputs and calculations, the current coordinates of the measuring lever (2) and the coordinates of the centroid of said figure; said display means (3) being adapted to show a zero difference when said measuring lever (2) is moved to the centroid of said figure. The apparatus according to claim 3 including marking needle means (2) on said measuring lever (2) adjacent said tracing means (6) said calculating means being adapted to calculate the differences between the coordinates on the said marking needle (7) means and the centroid of said figure; said display means (3) being adapted to display the differences of said coordinates and zero difference when said marking needle means (7) is positioned at the centroid of said two dimensioned figure.

Inventors: KAJI KATSUMI, NEMOTO HIROSHI, KAJI, KATSUMI, NEMOTO, HIROSHI, KAJI, KATSUMI, C/O USHIKATA MFG. CO., LTD., NEMOTO, HIROSHI, C/O USHIKATA MFG. CO., LTD.
Applicants: KUBO AKIO, KUBO, AKIO
Application year: 1994
Main classification: G01B5
IPC codes: G01B5